/Engine/Source/Runtime/Core/Public/Misc/Base64.h
Get the maximum decoded data size for the given number of input characters.
The maximum number of bytes that can be decoded from this input stream. The actual number of characters decoded may be less if the data contains padding characters. CallGetDecodedDataSize()with the input data to find the exact length.
static constexpr uint32 GetMaxDecodedDataSize ( uint32 NumChars )